Ettlingen, August 2002
Depending on its field of application, plastic film must have a special
diffusion behaviour. For this purpose, plastic granulate is mixed with a
high-boiling oil and is extruded as a film. The oil is then scrubbed from the
film by means of trichloroethylene so that a porous film is produced after
drying. The oil recovered must be free from solvent (< 0.1 %) so that it can
be reused for film production.
To this end, a single-effect falling film evaporator with downstream flash
column is used. In this system, trichloroethylene is first evaporated and then
separated.
The particular feature of this plant is the fact that the vacuum required
for this process is generated by two single-stage steam jet vacuum pumps which
are driven by the evaporated trichloroethylene vapour. Especially in the case
of solvents, steam vacuum pumps offer decisive technological and, above all,
economical advantages as compared to mechanical vacuum pumps. They are easy to
service, hard wearing and have a high working reliability. Thanks to the closed
circuit, jet vacuum pumps driven by product vapour are energetically favourable
and environmentally friendly. The investment costs are considerably lower
especially at higher suction rates.